The disclosure relates to an automatic transmission in which elements of a single planetary gear set connected to an input shaft are connectable with elements of a multiple planetary gear set via a clutch, in addition to being fixable via a brake, such that the rotation of the input shaft is shifted to multiple speeds and then transmitted to an output shaft.
An automatic transmission, disclosed in Japanese Patent Laid-Open Publication No. 4-219553 (paragraphs 0030 and 0034, and FIG. 3) (U.S. Pat. No. 5,106,352 is of the family of the Japanese Publication), is provided with a single planetary gear set and a multiple planetary gear set. The single planetary gear set has a first ring gear, a first sun gear fixed to a transmission case, and a first carrier supporting a pinion that meshes with the first sun gear and the first ring gear. Meanwhile, the multiple planetary gear set is provided with second and third sun gears, a long pinion, an intermediate pinion, a common carrier, and a common ring gear. The long pinion directly meshes with the second sun gear, and meshes with the third sun gear via the intermediate pinion. The common carrier supports the long pinion and the intermediate pinion, while the common ring gear meshes with the long pinion. In order to establish shift speeds including six forward speeds and one reverse speed, the common ring gear of the multiple planetary gear set is directly connected to an output shaft, and the rotation of the first carrier of the single planetary gear set (whose rotational speed is decelerated by the rotation of the input shaft) is selectively transmitted to the third and second sun gears of the multiple planetary gear set via first and third clutches. Additionally, the rotation of the input shaft is selectively transmitted to the multiple planetary gear set via a second clutch. The second sun gear and the common carrier of the multiple planetary gear set are selectively fixed by first and second brakes, respectively.
Disclosed in U.S. Pat. No. 5,542,889 (third and fourth columns, and FIG. 1) is an automatic transmission (see FIG. 1 of the U.S. patent) that has a single planetary gear set 52 structured such that a crankshaft 14 of an engine is directly connected to an impeller 12 of a torque converter 10, and a turbine 16 is directly connected to an input shaft 44. Moreover, a ring gear 72 rotates and accelerates the rotational speed of a carrier 74 directly connected to the input shaft 44, a fixed sun gear 70, and the input shaft 44. The automatic transmission also has multiple planetary gear sets 50, 48 structured such that a ring gear 64 and a carrier 58 of the two planetary gear sets 50, 48 are directly connected, and a carrier 66 and a ring gear 56 are connectable by a clutch CL1. The sun gear 62 of the multiple planetary gear sets 50, 48 is connectable with a carrier 74 via a clutch CL3, and fixable using a brake B2. Reverse rotation of the carrier 66 is prevented by a one-way clutch 82. Likewise, reverse rotation of the ring gear 56, which is connected to the carrier 66 via the clutch CL1, is also prevented by the one-way clutch 82. The carrier 66 is connectable with the ring gear 72 of the planetary gear set 52 via a clutch CL2, and fixable using a brake B1. Furthermore, the directly connected ring gear 64 and carrier 58 are also directly connected to an output shaft 90, and a sun gear 54 of the planetary gear set 48 is directly connected to the input shaft 44.
According to the automatic transmission described in Japanese Patent Laid-Open Publication No. 4-219553, the output rotation of the engine is decelerated by the single planetary gear set, and then input to the multiple planetary gear set, whereby torque increased by the multiple planetary gear set is transmitted. Furthermore, if the engine output characteristic outputs a high torque at a relatively low output rotation, for example, as in the case of a diesel engine, the transmitted torque further increases. Thus, an accompanying increase in the sizes of parts, and an increase in the capacities of clutches and brakes are required in order to handle the higher torque.
The automatic transmission described in U.S. Pat. No. 5,542,889 attempts to resolve such a problem, wherein rotation of the input shaft rotationally driven by the engine via a torque converter is first accelerated by the single planetary gear set 52 and then input to the multiple planetary gear sets 48, 50. A vehicle with high output torque at a low-speed rotation, such as one mounted with a diesel engine, starts moving by switching from the torque converter and gradually connecting a start clutch. However, the automatic transmission described in U.S. Pat. No. 5,542,889 is rotationally driven via the torque converter and thus cannot avoid a reduction in transmission efficiency due to transmission loss caused by the fluid. Furthermore, to ensure compatibility with variations of gasoline engines with high rotational speed and diesel engines with relatively low rotational speed requires changing the single planetary gear set inside the automatic transmission. This in turn requires many part changes, resulting in increased costs. As used herein “rotation” is representative of rotational speed and/or rotational torque.